Organic electronics using organic semiconductors of both high molecular and low molecular have noticed as a major next-generation technology for manufacturing flat panel displays and electronic paper. Recently, it has been highly progressed that an organic electric field light emission diode having been manufactured as a commercial reality and researches and developments for an organic semiconductor thin film electric field effect transistor for applying to an active-matrix-use switching element.
One of the features of the organic electronics is that it is possible to manufacture an electronic device by solution process without vacuum state and printing technique improved from the process. Compared with a conventional inorganic-based semiconductor device requiring high costs for a large-scale vacuum device, a high-temperature device, etc., due to manufacturing a product with larger size, it has been expected to be able to manufacture a flat panel display and electronic paper with a large area by reduced energy and low costs.
As technique constructing an organic semiconductor thin film by printing technique, an organic semiconductor of high molecular system of which the viscosity in a solution tends to increase has been researched. In contrast, an organic semiconductor of low molecular system obtaining higher device property compared with high molecular system is difficult to form a uniform semiconductor layer due to a low viscosity of a solution and a highly crystalline property possessed by the low molecular organic semiconductor.
As potent printing technique using an ink with relatively low viscosity, an ink jet printing method has been proposed (see JP Publication 2005-518332). The method for manufacturing an organic semiconductor thin film by the ink jet printing method comprises steps of dropping a solution (ink) dissolving a high concentration of an organic semiconductor in an organic solvent or the like onto a substrate from an ink head and depositing an organic semiconductor layer by the succeeding evaporation of the organic solvent. However, in this method, since the deposition of the organic semiconductor proceeds with generation of convection inside the droplet after dropping the ink, the deposition of the material is concentrated on the peripheral portion of the droplet where the solvent is mainly evaporated. The obtained thin film is only thin because a film thickness of the peripheral portion of the obtained film is very thick.
To improve the film forming property, method for suppressing the convection inside the droplet by mixing a soluble polymer such as poly(α-methylstyrene) or the like in the solution has been proposed (see Advanced Materials Vol. 21 p. 1166, 2009). It is shown that, since the solvent evaporation rate reduces by the effect of a high molecular matrix, it is effective because a larger microcrystal grain grown can be obtained.
Moreover, an attempt to improve the uniformity of the film thickness of the organic semiconductor layer by controlling the convection inside the droplet by mixing a different organic solvent has been reported (see Advanced Materials Vol. 18 p. 229, 2008). However, the method is not sufficient in terms that the property deteriorates because the polymer unrelated the conductivity is mixed with the low molecular organic semiconductor and of controllability, uniformity, etc. of the entire film formation obtained by dropping.
On the other hand, as an ink jet printing method for a low molecular organic material, a double shot-ink jet printing method using a molecular compound-based conductive organic material consisting of two kinds of molecules which are electron donating molecules and electron accepting molecules has been proposed (see JP Publication 2007-305807 and JP Publication 2008-153318). This method comprises the steps: preparing an ink obtained by dissolving a high concentration of the electron donating molecules and an ink obtained by dissolving a high concentration of the electron accepting molecules separately; mixing the inks from each ink head respectively discharging at the same position of a substrate; and mixing them applying onto the same position on the substrate to form a molecule compound thin film on the substrate. This method is reported that since the solubility of the molecule compound is extremely lower than the solubility of each molecule and the molecule compound is deposited prior to evaporation of the organic solvent, a thin film with high uniformity of film quality and film thickness can be obtained.
However, the above methods are limited in case in which in the molecule compound consisting of two kinds of molecules, a great difference in solubility between the material molecules and the compound can be utilized. Since low molecular organic semiconductors obtaining high device property is mostly organic materials consisting of single component organic molecules, the above-mentioned ink jet printing method cannot be applied to it.
Incidentally, in the organic semiconductor device, an organic semiconductor layer of a core layer for device operations applies an amorphous thin film with ruleless molecular arrangement or a polycrystalline thin film consisting of microcrystals of which molecules are regularly arranged with a size of several micrometers or less. Moreover, many researches on a monocrystal device using a monocrystal with a size of several hundred micrometers or more as a prototype device to search a carrier transfer state inside an organic semiconductor layer have been conducted. It has been reported that since the monocrystal device does not have grain boundary which is one of causes intervening with the carrier transfer and the regularity of a molecular arrangement is on the entire area of the semiconductor, a superior carrier transfer property can be obtained (see Science and Technology of Advanced Functional Materials, Vol. 10 p. 024314, 2009).
Moreover, recently, researches that a monocrystal device with superior property is configured on a substrate using a processing technique to effectively utilize as a practical device have been developed.
For example, Nature, Vol. 444, p. 913, 2006 proposed method for growing an organic semiconductor monocrystal only on a treated area by the vapor phase method, wherein the treated area is on a surface treated with a silane coupling agent by octadecyl triethoxysilane (OTS) selectively carried out only on the gaps between the electrodes in an arrangement of a large number of source-drain electrodes formed on a substrate.
Moreover, regarding a configuration of a monocrystalline organic semiconductor device using a solution method, Applied Physics Express, vol. 2, p. 111501, 2009 has proposed method comprises steps: contacting an end portion of a silicon wafer or the like for supporting droplets on a substrate with 2,7-dioctyl[1] benzothieno [3,2-b][1] benzothiophene (hereinafter, referred to as “C8-BTBT”) with a highly crystalline property; and gradually growing a C8-BTBT monocrystal by tilting the entire substrate.
However, the above methods are insufficient in terms of manufacturing a monocrystalline organic semiconductor thin film with good controllability in an industrially mass producible level. Moreover, regarding the application of a printing technique, in particular, for effectively utilizing property of organic electronics, no effective methods applicable to the monocrystalline organic semiconductor device have been known.